Heiresses/one-time couple Courtenay Semel and the late Casey Johnson are seen here in happier times two years ago in Marina Del Rey, as they lounged poolside in their bikinis, in new photos obtained exclusively by RadarOnline.com.

Semel, a rising star on the social circuit in Hollywood, Tweeted sad sentiments Tuesday about the shocking death of her ex-girlfriend, a mother of one who was just 30 when authorities discovered her lifeless body in a West Hollywood home.

Semel, whose father is ex-Yahoo! honcho Terry Semel, shared a passionate — and sometimes dangerous — relationship with the late Johnson & Johnson heiress, including a 2009 incident which she allegedly beat Casey up before setting her hair on fire. Semel also was the one who reported Johnson to police on burglary charges involving British model Jasmine Lennard in December.

“The truth is that she needs to get serious help,” Semel prophetically told the NY Post following Johnson’s arrest last month. “But what worries me is that she will hit rock bottom before she does that.”

Semel has also been romantically tied to Johnson’s fiancé at her time of death, Tila Tequila, and to Lindsay Lohan.